Le séminaire a lieu le Jeudi
31 mai 2001 de 11h00 à 12h00
dans la salle de réunion
du PHC (Observatoire de Nice).
Microinstabilities are widely believed to play a dominant
role for anomalous transport of
energy in tokamak plasmas.
Ion Temperature Gradient (ITG) driven modes, in particular,
have been extensively studied
in the past few years; the present global study, aims
to assess the role of electromagnetic
effects on the linear stability of these drift waves,
in the framework of gyrokinetic theory.
The model and the applied numerical method will be briefly
outlined.
A low-frequency electromagnetic perturbation is applied
to the equilibrium tokamak plasma.
Quasi-adiabatic electron dynamics is taken into account
with the drift-kinetic
approximation, including also trapped electrons.
The plasma is described by means of the quasi-neutrality
equation and the parallel
component of Ampère's law. The system of equations
is then solved over the whole
plasma domain, by means of a spectral approach.
Numerical results will be shown of the strong stabilization
of toroidal ITG modes induced
by electromagnetic effects, which occurs even when including
trapped electron dynamics.
An extension of the study to Trapped Electron Modes (TEM),
has instead shown that finite
ß has little influence on such drift waves. Finally
different magnetic shear profiles have
been analyzed to study the combined effect of ß
and magnetic shear.